Multiple categories management fails in admin

[devil1591]

In /wp-admin/categories.php, you can't make the following multiple categories structure :

MAIN SUB CAT
  — sub cat 1
    — — sub sub cat 1
  — sub cat 2
    — — sub sub cat 2

You can write posts and assign all theses categories, but you can't administrate them, "sub sub cat 2" becomes invisible.

Fixed by [5296] from #3985